Magnetophoretic and electromagnetophoretic displays

ABSTRACT

The present invention is directed to a display device which comprises two layers of insulating substrate, at least the substrate on the viewing side is transparent, an array of display cells sandwiched between the two layers of substrate, a writing means, and optionally an erasing means to magnetically or electrically erase the image. The display cells are filled with a dispersion of magnetic particles which may be charged or non-charged. The display of the invention eliminates the use of the transparent conductor film, such as ITO, on the viewing side. Therefore, the displays of this invention are more cost effective, more flexible and durable and capable of higher image contrast ratio and higher reflectance in the Dmin area.

This application is a continuation of U.S. application Ser. No.12/509,201, filed on Jul. 24, 2009 now U.S. Pat. No. 8,018,643, which isa continuation of U.S. application Ser. No. 11/510,285, filed on Aug.24, 2006, now U.S. Pat. No. 7,580,180, which is a continuation-in-partof U.S. application Ser. No. 11/149,678 filed on Jun. 8, 2005, now U.S.Pat. No. 7,113,323, which is a continuation-in-part of U.S. applicationSer. No. 10/394,488, filed on Mar. 20, 2003, now U.S. Pat. No.6,927,892, which claims the benefit of U.S. Provisional Application60/367,325, filed on Mar. 21, 2002; the contents of all the applicationsreferred to above are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

An electrophoretic display (EPD) is a non-emissive device based on theelectrophoresis phenomenon influencing charged pigment particlessuspended in a colored dielectric solvent. This general type of displaywas first proposed in 1969. An EPD typically comprises a pair ofopposed, spaced-apart plate-like electrodes, with spacers predetermininga certain distance between the electrodes. At least one of theelectrodes, typically on the viewing side, is transparent.

When a voltage difference is imposed between the two electrodes, thepigment particles migrate by attraction to the plate of polarityopposite that of the pigment particles. Thus, the color showing at thetransparent plate, determined by selectively charging the plates, can beeither the color of the solvent or the color of the pigment particles.Reversal of plate polarity will cause the particles to migrate back tothe opposite plate, thereby reversing the color. Intermediate colordensity (or shades of gray) due to intermediate pigment density at thetransparent plate may be obtained by controlling the plate chargethrough a range of voltages or pulsing time.

EPDs of different pixel or cell structures have been reportedpreviously, for example, the partition-type EPD (M. A. Hopper and V.Novotny, IEEE Trans. Electr. Dev., 26(8):1148-1152 (1979)) and themicroencapsulated EPD (U.S. Pat. Nos. 5,961,804 and 5,930,026).

An improved EPD technology was disclosed in U.S. Pat. No. 6,930,818(corresponding to WO 01/67170 published on Sep. 13, 2001), U.S. Pat. No.6,672,921 (corresponding to WO 02/65215 published on Aug. 22, 2002) andU.S. Pat. No. 6,933,098 (corresponding to WO 02/01281 published on Jan.3, 2002), all of which are incorporated herein by reference. Theimproved EPD comprises isolated cells formed from microcups ofwell-defined shape, size and aspect ratio and filled with chargedparticles dispersed in a dielectric solvent or solvent mixture,preferably a halogenated solvent, particularly a perfluorinated solvent.The filled cells are individually sealed with a polymeric sealing layer,preferably formed from a composition comprising a material selected fromthe group consisting of thermoplastics, thermosets and precursorsthereof.

All of the previously known and the microcup-based electrophoreticdisplays may be constructed into the form of a board to be used ase-signs or e-bulletins. However, the use of a transparent conductorfilm, such as indium tin oxide (ITO) on the viewing side, particularly atransparent patterned conductor film, in such large displays is aneconomic disadvantage as the transparent conductor film is expensive.The expense for the transparent conductor film often is a major part ofthe total manufacturing cost of the electrophoretic displays. Inaddition, the ITO film is brittle and only provides about 80-90% oftransmission or reflection in the visible light region. Therefore, thereis still a need for a solution to these issues.

SUMMARY OF THE INVENTION

The display of the present invention comprises two layers of insulatingsubstrate, at least one of which, usually the one on the viewing side,is transparent, and an array of display cells sandwiched between the twolayers of insulating substrate. The display may optionally comprise aconductive layer placed between the array of cells and one of thesubstrate layers.

In one embodiment, the insulating substrate layers are dielectricsubstrate layers.

The display cells are filled with an electromagnetophoretic fluid inwhich magnetic particles are dispersed in a liquid medium. The particlespreferably are prepared from highly magnetic compounds and metals oralloys. The liquid medium may comprise a contrast colorant, which may bea dye or pigment. In one embodiment, the magnetic particles may besuspended in air.

In one embodiment of this invention, the magnetic particles are coloredor blackened and the contrast color pigment in the liquid medium iswhite such as TiO2 and ZnO. The magnetic particles or the white contrastpigment particles may be charged or non-charged. If both the magneticparticles and the white contrast particles are charged, they shouldeither carry charges of opposite polarity or carry charge of the samepolarity but different charge density so that enough discrimination ofelectrophoretic mobility between the two type particles exists.

In another embodiment of the invention, magnetic particles having a highsurface reflectivity are dispersed in a liquid medium which furthercomprises a colorant of a contrast color. Metal and paramagneticparticles such as stainless steel, Fe—Co, Fe—Ni, Fe—Co—Ni, Ni—Co, Co—Cror Fe—Co—V alloy particles are particularly useful in this case. Themagnetic particles may be charged or non-charged. The colorant forgenerating color of the liquid medium may be a dye or a pigment whichmay also be charged or non-charged.

The device may further comprise a writing means, such as a magnetic pen,a magnetic writing head, a high voltage electric writing head or a highvoltage pen, for generating an image. The writing means may be on theviewing side or behind the non-viewing side.

The device may also optionally comprise an erasing means to magneticallyor electrically erase an image. The erasing means may also be placed onthe viewing side or behind the non-viewing side.

Similar to conventional electrophoretic displays (EPDs or EPIDs), theelectromagnetophoretic displays (EMPDs) of this invention are bistableand have a very wide viewing angle. Many different driving mechanismsand circuitry designs may be employed to achieve optimum performance ofthe displays of this invention. Most of them do not require the use of atransparent conductor film, such as ITO film, which is expensive,fragile and often transmits or reflects less than 90% of the incipientvisible light. As a result, the displays of the invention are much moreflexible and durable than conventional displays and provide images of ahigh contrast ratio, wide viewing angle and high reflectance in the Dminarea. Furthermore, the present invention provides a great number ofalternatives in design, and a particular type of design within the scopeof the invention may be easily constructed to meet the needs for avariety of applications.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1, 2, 3A, 3B, and 4-9 depict a variety of designs for themagnetophoretic and electromagnetophoretic display of the invention.

FIG. 10 depicts a preferred embodiment of the present invention in whichthe cells are individually sealed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a display device, which comprisestwo layers of substrate, at least the viewing side is transparent, andan array of display cells sandwiched between the two layers ofsubstrate. In the context of this application, the term “viewing side”refers to the side seen by the viewer whereas the term “non-viewing”side refers to the side opposite from the viewing side.

In one embodiment, the two substrate layers may be insulating ordielectric layers, such as microporous organosilicates, ceramic,aluminum oxide, titanium dioxide, glass and polymeric sheets, plates orfilms prepared from poly(ethylene terephthalate), poly(ethylenenaphthalate), polycarbonate, polysulfone, polyimide, epoxy, phenolic,acrylics, unsaturated polyester, polyamide, polyurethane, polyurea andcomposites thereof. In the embodiments of this invention where anelectric field is used to drive or erase an image, a conductive layer onthe substrate is needed. Suitable conductive layers include Al, Cu, Au,Ag, Ni, Sn, ITO (Indium Tin Oxide) and alloys or composite filmsthereof.

The display cells sandwiched between the two layers of substrate may bethe conventional type of display cells (e.g., the partition-type cells),the microcapsule-based cells (prepared according to U.S. Pat. Nos.5,961,804 and 5,930,026) or the cells prepared according to the microcuptechnology disclosed in U.S. Pat. No. 6,930,818 and relatedapplications.

The display cells are filled with a magnetophoretic orelectromagnetophoretic fluid comprising magnetic particles dispersed ina liquid medium. The magnetic particles may be dispersed in the liquidmedium by any of the well-known methods, including grinding, milling,attriting, microfluidizing and ultrasonic techniques. For example,magnetic particles in the form of a fine powder are added to the liquidmedium and the resulting mixture is ball milled or attrited for severalhours to break up the highly agglomerated dry pigment powder intoprimary particles.

Low vapor pressure, non-hygroscopic solvents or solvent mixtures may beused as the liquid medium. Examples of useful solvents includehydrocarbons such as decahydronaphthalene (DECALIN),5-ethylidene-2-norbornene, fatty oils, paraffin oil, aromatichydrocarbons such as toluene, xylene, phenylxylylethane, dodecylbenzeneand alkylnaphthalene, low viscosity polyethers such as polypropyleneglycols and block copolymers of ethylene glycol and propylene glycol,low viscosity silicone oils, alkyl or alkylaryl esters and ketones,halogenated solvents such as perfluorodecalin, perfluorotoluene,perfluoroxylene, dichlorobenzotrifluoride,3,4,5-trichlorobenzotrifluoride, chloropentafluoro-benzene,dichlorononane and pentachlorobenzene, perfluorinated solvents such asFC-43, FC-70 and FC-5060 from 3M Company, St. Paul Minn., low molecularweight halogen containing polymers such as poly(perfluoropropyleneoxide) from TCI America, Portland, Oreg., poly(chlorotrifluoroethylene)ssuch as Halocarbon Oils from Halocarbon Product Corp., River Edge, N.J.and perfluoropolyalkylether such as Galden from Ausimont or Krytox Oilsand Greases K-Fluid Series from DuPont, Del. In one embodiment,poly(chlorotrifluoroethylene) may be used as the liquid medium. Inanother embodiment, poly(perfluoropropylene oxide) may be used as theliquid medium.

Sedimentation or creaming of the pigment particles may be eliminated bymicroencapsulating the particles with suitable polymers to match thespecific gravity to that of the liquid medium. Microencapsulation of thepigment particles may be accomplished chemically or physically. Typicalmicroencapsulation processes may include interfacial polymerization,in-situ polymerization, phase separation, coacervation, electrostaticcoating, spray drying, fluidized bed coating and solvent evaporation.Well-known procedures for microencapsulation have been disclosed inKondo, Microcapsule Processing and Technology, Microencapsulation,Processes and Applications, (I.E. Vandegaer, ed.), Plenum Press, NewYork, N.Y. (1974), and in Gutcho, Microcapsules and MicroencapsulationTechniques, Noyes Data Corp., Park Ridge, N.J. (1976), both of which arehereby incorporated by reference.

In addition to solvents or solvent mixtures, the term “liquid medium”,in the context of this invention, may include other substances that havea tendency to flow, such as melted wax. After being filled into thedisplay cells, the liquid medium may change its physical statetemporarily or permanently (i.e., turned into a solid, semi-solid orelastic state).

The magnetic or electromagnetic particles may also be suspended in airin the form of free flowing power.

Magnetic particles prepared from highly magnetic compounds and metals oralloys are preferred. Examples of magnetic materials useful in thisinvention include gamma ferric oxide, acicular magnetite,cobalt-modified or adsorbed ferric oxide, berthollide ferric oxide,chromium dioxide, metals or alloys (such as stainless steel, Fe—Co,Fe—Ni, Fe—Co—Ni, Co—Ni, Co—Cr and Fe—Co—V alloys), organic polyradicals(such as polymers with organic radicals in the side chain, main-chainconjugated polymers with organic radicals, two dimensional polyradicals,polymers containing paramagnetic metalloporphyrins as side chains andpolymers containing paramagnetic metal ions, e.g., Cu(II), Ni(II),Mn(II) or VO(II), in the main chain). Other useful magnetic materialscan be found in references such as “Magnetic Recording Handbook” byMarvin Camras; Van Norstrand Reinhold Co., (1988); and M. Kamachi“Magnetic Polymers” in “Functional Monomers and Polymers”, ed. By K.Takemoto, R. M. Ottenbrite and M. Kamachi; Marcel Dekker, Inc., (1997),the contents of which are incorporated herein by reference.

Specific examples of organic polyradicals include, but not limited to,those shown in the references identified above and several U.S. Pat.Nos. (e.g., 4,631,328, 4,594,400, 4,552,928 and 4,769,443), the contentsof which are incorporated herein by reference. Organic polyradicalsshown by Kamachi in “Magnetic Polymers” may include those containing2,2,6,6-tetramethylpiperidine-1-oxyl as a side chain, thermally annealedpolyphenylacetylene, those with phenoxy or nitroxy radicals,poly(1,3-phenyleneethynylene) with pendant nitronyl nitroxide ort-butylnitroxyl, two-dimensional polymers, such as that obtained byreacting 1,3,5-triaminobenzene with iodine, those with a repeating unitderived from indigo, those obtained from the catalyst-free 1,3-dipolarcycloaddition of 1,3-bis-(3-sydnone) andN′,N′-(1,4-phenylene)bismaleamide, those containing paramagnetic ionseither in the side chain or in the main chain. Those containingparamagnetic ions in the side chain include compounds containingtetraphenylporphyrin (TPP) moieties, especially those derived fromparamagnetic metal ions, for example, Cu(II), Ag(II), VO(II) and Co(II),and that derived from the reaction of TPP-Mn(II) and tetracyanoethylenein toluene, Those containing paramagnetic ions in the main chain includea heterobinuclear complex of Cu(II) and VO(II), an inorganic polymer,MnCu(pbaOH)(H₂O)₃ with regularly alternating magnetic centers, wherepbaOH is 2-hydroxy-1,3-propylenebis(oxamato), polymers composed of2-substituted 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and derivedfrom Cu(II), Ni(II) or Mn(II), linear chain polymers of M(hfac)₂(NIT)Rwhere M is Cu(II), Ni(II) or Mn(II), (NIT)R is2-alkyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and hfac ishexafluoroaceteylacetonate, and three dimensional structures, such as(rad)₂Mn₂-[Cu(opba)]₃(DMSO)₂:2H₂O, where rad is2-(4-N-methylpyridinium)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide,opba is o-phenylenebis(oxamato) and DMSO is dimethyl sulfoxide. Otherpolymeric radical containing compounds, (with the identity of theradical and its location indicated in the parentheses), are thosedescribed in U.S. Pat. No. 4,631,328 (various anthraquinone, stilbene,mono-, bis- or tris-azo dyes, side chain), U.S. Pat. No. 4,594,400(thioxanthone, side chain), U.S. Pat. No. 4,552,928 (di- andtriphenylamine, side chain) and U.S. Pat. No. 4,769,443 (piperidine,side chain). Some of these organic polyradicals may be prepared byincluding radical precursors in the prepolymer mixture, effectingpolymerization and then conversion to the radicals.

In one embodiment of this invention, contrast colorant particles aremagnetized by coating the colorant particles (e.g., TiO₂, ZnO, ororganic pigments such as carbon black, phthalocyanine and other organicpigments) with a magnetic material by, for example, sputtering, vacuumdeposition, electrodeposition, electroplating or electroless plating.

In another embodiment of this invention, the colorant pigment particlesare microencapsulated in a polymer matrix and the magnetic particles aremixed with the colorant pigment particles before the microencapsulationprocess. Submicron magnetic or metal particles are the most preferred inthis case.

In a further embodiment of this invention, the colorant particles aremagnetized by coating or encapsulating the particles with an organicpolyradical or magnetic polymer mentioned above.

The magnetized particles may be charged or non-charged. Similarly, thecontrast colorant particles may also be charged or non-charged. For thecharged particles, they may exhibit a native charge, or may be chargedexplicitly using a charge control agent, or may acquire a charge whensuspended in the suspending medium. Suitable charge controlling agentsare well known in the art; they may be polymeric or non-polymeric innature, and may also be ionic or non-ionic. Particles having high imagebistability, low viscosity, and high dispersion stability againstsedimentation, creaming, flocculation and network formation arepreferred.

For simplicity, colors of white or black are used to illustrate thefigures in the following. However, the colors may also be referred to as“a first color” or “a second color” and the two colors may becontrasting colors.

FIG. 1 depicts a magnetophoretic display of the present invention. Adisplay cell (11) is sandwiched between two layers of substrate (12 and13). At least one of the two layers is transparent and the transparentlayer (12) is on the viewing side. The cell is filled with a reflectiveor white (the primary color), non-charged magnetic particles (14)dispersed in a clear (contrast) color solution. Useful magneticparticles for this case include metal particles or metallized particlesprepared by, for example, sputtering, vacuum deposition,electrodeposition, electroplating, electroless plating, magnetic polymercoated or microencapsulated white pigments particles such as TiO₂ andZnO, and microcapsules containing a mixture of white pigments andmagnetic particles, particularly metal particles. Dyes or colorantpigments having a particles size well below the visible light scatteringrange (0.2-0.4 micrometer) are useful for preparing the clear contrastcolor solution.

Initially by applying a magnetic eraser (15) placed on the viewing side(12) of the display, all the reflective or white (primary color)magnetic particles are attracted to the viewing side, resulting in thecolor of the particles as the background seen by the viewer. A magneticwriting head (16), in this design, is placed behind the non-viewing side(13). The writing head is controlled by a PC or a tablet (not shown).When the writing head is turned on, the white particles are attracted tothe non-viewing side. For the areas where the white or reflectiveparticles are on the non-viewing side, the color of the dispersionmedium (i.e., the contrast color) is seen from the viewing side, thuscreating a contrast color-on-white or contrast-on-primary color image.

FIG. 2 illustrates an alternative embodiment of the invention in whichthe cell is also filled with non-charged, reflective or white (primarycolor) magnetic particles (24) dispersed in a clear contrast colorsolution. In this design, a magnetic eraser device (25) is placed behindthe non-viewing side (23). Initially the eraser attracts the white orreflective magnetic particles to the non-viewing side which generates acontrast background color (i.e., the color of the dispersion medium)seen from the viewing side. In this design, the image may be created bya magnetic writing device or writer (26) placed on the viewing side.When the writer (26) is turned on and the eraser (25) is turned off, thewhite or reflective magnetic particles are attracted to the viewingside, thus generating a white-on-contrast color or primary-on-contrastcolor image. Alternatively, a magnetic pen (26 a, on the viewing side)may be used instead of the magnetic writing head (26) to create the sameimage discrimination.

FIG. 3 illustrates another alternative embodiment in which the cell isfilled with charged, white (primary color) or reflective magneticparticles (34) dispersed in a clear solvent of a contrast color. Adisplay cell (31) is sandwiched between two layers of substrate (32 and33). At least one of the two layers is transparent and the transparentlayer (32) is on the viewing side. However, in this case, a layer ofconductor film (38) is placed between the cell (31) and the layer ofsubstrate (33) on the non-viewing side. A magnetic eraser (35) is placedon the viewing side. By applying the magnetic erasing means, the whiteor reflective magnetic particles are attracted to the viewing side thusgenerating a white or primary color background. In this design, an imagemay be created by either a magnetic writing head (36 a) placed behindthe non-viewing side (FIG. 3A) or a high voltage electric writing head(not shown in FIG. 3B) or a high voltage electric pen (36 b) on theviewing side (FIG. 3B) In the first scenario, when the magnetic writinghead is applied, it attracts the white (primary color) particles to thenon-viewing side thus creating a contrast color-on-white (or on primarycolor) image. In the second scenario when a high voltage electricwriting head or electric pen is used, an image may be created byapplying appropriate voltages to the electric pen and the conductor filmlayer (38). For example, if the conductor film has polarity oppositefrom the particles and the electric writing head or pen has the samepolarity as the particles, the white or primary color particlesinevitably migrate to the non-viewing side thus also generating acontrast color-on-white (or primary color) image. This embodiment is oneof the preferred.

There are still further embodiments of the present invention in which amixture of black or colored magnetic particles and white, non-magneticparticles are dispersed in a colorless clear solvent. The particles maybe charged or non-charged. If both types of particles are charged, it ispreferable to have the same polarity. These designs are illustratedbelow.

In the design as illustrated in FIG. 4, both types of particles arenon-charged. The design does not comprise a conductive film layer. Amagnetic eraser (45) is placed behind the non-viewing side. When theeraser head is applied, the black or color magnetic particles areattracted to the non-viewing side while the white non-magnetic particlesare randomly dispersed in the dispersion medium, thus creating a whitebackground color. The writing means (46) in this design is placed on theviewing side and the writing means may be either a magnetic writing heador a magnetic pen. When the magnetic writing head or the magnetic pen isturned on, the black or color magnetic particles are attracted to theviewing side thus generating a black (contrast color)-on-white image.This is also one of the preferred embodiments.

FIG. 5 illustrates an embodiment of the present invention in which amixture of charged, black or color magnetic particles and charged, whitenon-magnetic particles are dispersed in a colorless clear solvent. Thisdesign also comprises a conductive film layer (58). In this case, anelectric erasing means (55) is placed on the viewing side and it may bea high voltage electric eraser head or a manual high voltage electriceraser. The white and black particles may carry opposite charge polarityor the same polarity. If they are of the same polarity, the two types ofparticles should have enough difference in electrophoretic mobility forimage discrimination. The conductive film layer (58) has polarityopposite from the black particles and the electric erasing means has thesame polarity as the black particles. As a result, the black or colormagnetic particles migrate to the non-viewing side because of theelectric force and the white particles either migrate to the viewingside or, to a large degree, remain randomly dispersed in the dispersionmedium, thus creating a white background. The white background may alsobe achieved by applying a magnetic erasing means from the non-viewingside. The writing means (56) in this embodiment is also on the viewingside and it may be either a magnetic writing head or a magnetic pen.When the magnetic writing means is applied, it attracts the blackmagnetic particles to the viewing side thus generating a black (contrastcolor)-on-white image.

Alternatively, the display may have a mixture of charged, black orcontrast color magnetic particles and non-charged, white non-magneticparticles dispersed in a colorless clear solvent, as shown in FIG. 6.When an electric erasing means (65) is applied from the viewing side(provided that the conductive film layer has a charge polarity oppositeto that of the black or color particles and the electric erasing meanshas the same polarity), only the black or color particles migrate to thenon-viewing side and the white particles are randomly dispersed in thedispersion medium, generating a white background color seen from theviewing side. The white background may also be achieved by applying amagnetic erasing means from the non-viewing side. The writing means (66)in this design is also on the viewing side and it may be a magneticwriting head, a magnetic pen, a high voltage electric writing head or ahigh-voltage writing pen. As shown in FIG. 6, when the magnetic writingmeans is applied, it attracts the black or contrast color magneticparticles to the viewing side thus generating a black (contrastcolor)-on-white image. When an electric writing means having theopposite polarity from the black particles is applied, the writing meansattracts the black particles to the viewing side, thus also generating ablack (contrast color)-on-white image.

FIG. 7 illustrates another embodiment of the present invention. Thisdesign employs a mixture of non-charged, white or reflective magneticparticles and non-charged, contrast color or black non-magneticparticles dispersed in a colorless clear solvent. The design does notcomprise a conductive film layer. A magnetic eraser head (75) is placedbehind the non-viewing side. When the eraser head is applied, the whitemagnetic particles are attracted to the non-viewing side while the blackor color non-magnetic particles are randomly dispersed in the dispersionmedium, thus creating a black or contrast color background. The writingmeans (76) in this design is placed on the viewing side and the writingmeans may be either a magnetic writing head or a magnetic pen. When themagnetic writing head or the magnetic pen is turned on, the white orreflective magnetic particles are attracted to the viewing side thusgenerating a white (reflective)-on-black (contrast color) image.

FIG. 8 illustrates a further embodiment of the present invention. Inthis embodiment, a mixture of charged, white or reflective magneticparticles and charged, black or contrast color non-magnetic particlesare dispersed in a colorless clear solvent. The design also comprises aconductive film layer (88). In this case, the erasing means (85) isplaced on the viewing side and it may be a high voltage electric eraserhead, a manual high voltage electric eraser, a magnetic eraser head or amanual eraser head. In one scenario, the two types of particles maycarry opposite charges, the conductive film layer has same polarity asthe white or reflective magnetic particles and the electric erasingmeans has the opposite polarity. In other words, the conductive filmlayer has polarity opposite of the black or color non-magnetic particlesand the electric erasing means has the same polarity as the blacknon-magnetic particles. As a result, the white or reflective particlesmigrate to the viewing side by the electric force creating a white orreflective background color. In another scenario, the white orreflective background color may also be created by a magnetic erasingmeans placed on the viewing side. The writing means (86) in thisembodiment is also on the viewing side and it may be either a highvoltage writing head or a high voltage pen. When the electric writingmeans is applied, it attracts the black or contrast color non-magneticparticles to the viewing side (provided that the electric writing meanshas the same polarity as the white or reflective magnetic particles; butopposite polarity to the black or color non-magnetic particles), thusgenerating a black (contrast color)-on-white (reflective) image. This isalso one of the preferred embodiments.

Alternatively, the black or contrast color non-magnetic particles inthis design are non-charged or carry a charge of the same polarity asthe magnetic particles, but with a significantly lower electrophoreticmobility. As a result, in the scenario illustrated in FIG. 9, when anelectric erasing mean (95) is applied from the viewing side (providedthat the conductive film layer has opposite polarity as the white orreflective magnetic particles and the electric erasing means has thesame polarity), only the white or reflective particles migrate to thenon-viewing side and the black or contrast color particles remainrandomly dispersed in the dispersion medium, generating a black orcontrast color background seen from the viewing side. The black orcontrast color background may also be achieved by applying a magneticerasing means from the non-viewing side. The writing means (96) in thisembodiment is also on the viewing side and it may be a magnetic writinghead, a magnetic pen, a high voltage electric writing head, or ahigh-voltage writing pen. As shown in FIG. 9, when the magnetic writingmeans is applied, it attracts the white or reflective particles (whichare magnetic) to the viewing side thus generating a white(reflective)-on-black (contrast color) image. When an electric writingmeans is applied, the white or reflective particles may also beattracted to the viewing side generating a white (reflective)-on-black(contrast color) image.

FIG. 10 depicts a preferred embodiment of the present invention. Thecells (100) are sandwiched between the two layers of substrate (102 and103) and of well-defined size, shape and aspect ratio and areindividually sealed with a polymeric sealing layer (104). The cells havepartition walls (107) which separate the electromagnetophoretic fluid(101). The display may optionally comprise an additional adhesive layer(not shown) between the substrate (102) and the polymeric sealing layer(104). The particles (105) suspended in the electromagnetophoretic fluid(101) are magnetized and optionally charged. The electromagnetophoreticdisplay (EMPD) of this invention may further comprise a polymeric layer(not shown) between the substrate (103) and the electromagnetophoreticfluid (101). The “microcup” based cells may be prepared by amicroembossing process or by photolithography as described in WO01/67170and related applications. There may be a conductor film layer (106)optionally placed between the cells (100) and one of the two substratelayers (102 & 103). The device as described has a recording means andoptionally an erasing means as depicted in FIGS. 1-9.

The formation of the sealing layer (104) is carried out by any of themethods disclosed in U.S. Pat. No. 6,930,818, the content of which isincorporated herein by reference in its entirety. Briefly, themicrocup-based cells filled with an electromagnetophoretic fluid aresealed with a polymeric sealing layer. The polymeric sealing layer maybe formed from a sealing composition having a specific gravitypreferably lower than that of the electromagnetophoretic fluid. In onemethod, the sealing is accomplished by dispersing the sealingcomposition into the electromagnetophoretic fluid before filling andafter filling, the sealing composition forms a supernatant layer on topof the electromagnetophoretic fluid, after which, the polymeric sealinglayer is hardened by solvent evaporation, interfacial reaction,moisture, heat or radiation. In another method, the sealing isaccomplished by overcoating the electromagnetophoretic fluid with thesealing composition and the sealing is then accomplished by hardeningthe sealing composition by solvent evaporation, interfacial reaction,moisture, heat, radiation or a combination of these curing mechanisms.In both methods, the polymeric sealing layer is hardened in situ (i.e.,when the sealing composition is in contact with theelectromagnetophoretic fluid).

The embodiments specifically exemplified above are clearly notexhaustive. It should be understood that various magnetophoresis andelectro-magnetophoresis may be constructed by varying the followingelements:

1) magnetic particles of one single color which may be

-   -   i) charged; or    -   ii) non-charged;

2) two types of color (primary color and contrast color) particles, oneof which is magnetic and

-   -   a) both types of particles are non-charged;    -   b) only one of them is charged;    -   c) both are charged; but carrying opposite charges    -   d) both carry charges of the same polarity but one of them has a        significantly higher electrophoretic mobility than the other.

3) color of the solvent in which the particles are dispersed;

4) an electric erasing means or magnetic erasing means

5) the erasing means may be on the viewing or non-viewing side

6) an electric writing means or a magnetic writing means

7) the writing means may be on the viewing or non-viewing side.

For example, the magnetic particles may comprise white magneticparticles and magnetic particles of a contrast color. The two types ofmagnetic particles may be suspended in a clear and colorless liquidmedium or in air. In one embodiment, the white magnetic particles arecharged and the magnetic particles of the contrast color arenon-charged. In another embodiment, the white magnetic particles arenon-charged and the magnetic particles of the contrast color arecharged. In a further embodiment, the magnetic particles are white andthe dispersion further comprises charged non-magnetic particles of acontrast color. In still a further embodiment, the white magneticparticles are charged. In still a further embodiment, the white magneticparticles are non-charged.

It is also possible that the magnetic particles in the dispersioncomprise black magnetic particles and magnetic particles of a contrastcolor. The two types of magnetic particles are suspended in a clear andcolorless liquid medium or in air. In one embodiment, the black magneticparticles are charged and the magnetic particles of the contrast colorare non-charged. In another embodiment, the black magnetic particles arenon-charged and the magnetic particles of the contrast color arecharged. In a further embodiment, the magnetic particles are black andthe dispersion further comprises charged non-magnetic particles of acontrast color. In still a further embodiment, the black magneticparticles are charged. In still a further embodiment, the black magneticparticles are non-charged.

When two types of magnetic particles are present in the dispersion, itis preferred that the two types of magnetic particles have differentmobility. For example, the magnetic particles may be “paramagnetic”,“ferrimagnetic”, “ferromagnetic” and “diamagnetic”. The first three maybe attracted to a magnetic with increasing positive susceptibility andthe diamagnetic may be repelled (negative susceptibility). In otherwords, if both types of particles are magnetic, it is preferred that themagnetic particles have different susceptibility between the two typesto show differentiation in mobility in the magnetic field.

In this invention, when referring to particles of a particular color(e.g., white, black or “a first color”, etc.), it means thatpredominantly the particles are of that color. It is also noted that aparticular color may be achieved by mixing particles of differentcolors. For example, a black color may be achieved by a mixture ofparticles of red, green and blue colors in various proportions.

The various combinations of the elements are intended to be within thescope of the claims appended hereto.

What is claimed is:
 1. An image display comprising: (i) cells filledwith a dispersion comprising particles suspended in a liquid medium,wherein the particles consist of magnetic particles and non-magneticparticles, both are charged; (ii) writing means; and (iii) erasingmeans, wherein the magnetic particles are antiferromagnetic particles.2. The display of claim 1, wherein the liquid medium is a solvent orsolvent mixture.
 3. The image display of claim 1, wherein the writingmeans is an electric writing means or a magnetic writing means.
 4. Theimage display of claim 1, wherein the erasing means is an electricerasing means or a magnetic erasing means.
 5. An image displaycomprising: (i) cells filled with a dispersion comprising particlessuspended in a liquid medium, wherein the particles consist of magneticparticles and non-magnetic particles, both are charged; (ii) writingmeans; and (iii) erasing means, wherein the magnetic particles areparamagnetic particles.
 6. The display of claim 5, wherein the liquidmedium is a solvent or solvent mixture.
 7. The display of claim 5,wherein the writing means is an electric writing means or a magneticwriting means.
 8. The display of claim 5, wherein the erasing means isan electric erasing means or a magnetic erasing means.